The present invention relates to a transmission mechanism for tractor in which power from the rotary drive shaft interlocking with the engine is transmitted, through double action clutch means, to the travelling system rotary shaft projecting from the transmission case and to the power take-off or PTO system rotary cylindrical shaft co-axially fitted on the external periphery of the projecting end of the travelling system rotary shaft.
As agricultural tractors, there is a first typed one in which power ON/OFF operations of the travelling system and the PTO system may be carried out at the same time by a main clutch, so that, when the tractor is stopped travelling, the PTO system is always stopped driving. There is a second typed tractor in which the interlocking mechanism for operation means is simplified and power ON/OFF operations of the travelling system and the PTO system may be carried out in succession by double action clutch means, thereby to readily carry out such an operation as preferentially stopping the travelling system or the PTO system prior to the other.
In forming a double action clutch typed tractor of the second type as described above, particular structural modification to be made to the transmission case is required for mounting double action clutch means. Namely, a single clutch typed tractor transmission case of the first type as described above may not be utilized for a double action clutch typed tractor transmission case. When intending to manufacture tractors of the both types as described above, transmission cases specifically designed for each typed tractor are therefore required. Two manufacturing lines each for each typed tractor are subsequently necessary, thus resulting in extended and expensive manufacturing facilities and increased costs.